The invention relates generally to the chemical detection of halogenated hydrocarbons (halohydrocarbons) and more particularly to the detection of halohydrocarbons, including certain organic chlorides, using a Fujiwara-like reaction.
Trichloroethylene (TCE) heads the U.S. Environmental Protection Agency's (EPA) list of hazardous (toxic, carcinogenic, etc.) compounds and the organic chlorides, as a group, dominate the ten (10) most frequently found dangerous compounds. The other organic chlorides include 1,1,1-trichloroethane (TCA), 1,1,2,2-tetrachloroethane, chloroform (CHCl.sub.3), carbon tetrachloride (CCl.sub.4) and 1,2-dichloroethylene (DCE). Thus, the detection of these compounds is extremely important.
The Fujiwara reaction is a known methodology widely used for the fluorometric and colorimetric analysis of gem-polyhalogen compounds. In the presence of a strong alkali (OH.sup.31), such as sodium or potassium hydroxide, pyridine or a derivative thereof reacts with a halogenated hydrocarbon to produce a red colored fluorescent product. The traditional chemistry (pyridine/alkali metal base) is a two-phase system, since the commonly used alkalis (NaOH or KOH) in water are insoluble in pyridine. Therefore, the reaction product is formed only at the interface. The Fujiwara chemistry has been modified to overcome the limitations of the two-phase system. U.S. Pat. No. 4,929,562 to Anderson (deceased) et al. shows a single-phase system which utilizes pyridine or a derivative thereof with a hindered nitrogen base (phase transfer catalyst), particularly a tetraalkyl ammonium hydroxide (quaternary ammonium base). The larger bases (because of the larger cations) have increased solubility in pyridine so that a single phase is achieved. However, the bases are still inorganic bases, i.e., OH.sup.- is the base. The chemistry is not particularly compound specific but is species specific.
A major problem with the Fujiwara (pyridine/base) reaction is the problem of competing pathways for the carbene reaction intermediate. Water, the typical solvent for inorganic bases, consumes the carbene, thereby preventing completion of the preferred reaction with pyridine. Therefore, it is desirable to modify or improve the conventional Fujiwara chemistry to eliminate the problems of the prior art. Also, pyridine is an offensive-smelling hazardous material. Its derivatives, although not as bad as pyridine itself, are not soluble in water to an appreciable extent. Therefore, it is very important to develop a non-aqueous system in order to employ pyridine derivatives in place of pyridine. Also, liquid pyridine is not amenable to fabrication of a solid state sensor, so developing a pyridine derivative based system is also important for solid state applications.